Tubular burner for industrial furnaces

ABSTRACT

A tubular burner for industrial furnaces is capable of achieving a good mixing of combustion gas and fuel. This burner contains an end section projecting into a combustion zone supplied with secondary combustion air, and several separate annular feed ducts for combustion gas and fuel bounded by tubular walls arranged coaxially one inside the other, individual nozzles being arranged in approximately annular distribution in the end wall of the combustion gas feed duct facing into the combustion zone. To achieve a good mixing of combustion gas/combustion air and fuel, at least one outer annular feed duct is constructed essentially as fuel feed duct, whilst the combustion gas feed duct equipped with individual nozzles is arranged radially inside this fuel feed duct.

The invention relates to an industrial furnace having a tubular burner,in accordance with the preamble to claim 1.

A particularly preferred field of application for such an industrialfurnace is in installations for the heat treatment of mineral goods, forexample, furnaces or furnace systems for the heat treatment or calciningof cement clinker, lime, ores and so on; industrial furnaces andindustrial furnace systems that come into consideration are inparticular rotary tubular kilns, calcining furnaces and calcininginstallations etc.

It is exactly with industrial furnaces of the above-mentioned kind thatit is important that the process of combustion can be influenced by theconfiguration and mode of operation of the burner, in order to be ableto carry out the industrial processes in such industrial furnaces orfurnace systems, for example, to be in with the particular properties ofthe raw material, the desired quality features of the product to beproduced, different types of fuel and so on. Furthermore, at the sametime the stipulated emission values of such industrial furnaces, forinstance in respect of carbon dioxide and nitrogen oxide, must also beadhered to, wherein it is desirable for the associated burner, and hencealso the corresponding furnace, to be operated in an energy-efficientand cost-effective manner. To that end, efforts have been made todevelop an optimum flame in the furnace combustion zone by means of theburner, by effecting favourable mixing of the incoming combustion air orthe incoming combustion gas with the incoming fuel.

Different burner constructions are therefore already known (e.g. DE-A-4319 363 and DE-A-196 48 981), in which several coaxially arranged tubewalls define several separate feed ducts of approximately annularcross-section for combustion gas or combustion air and fuel. In thisconnection, at the burner front end of the outer annular feed ductintended for the supply of combustion gas, the end discharging into thecombustion zone, there are arranged individual nozzles in approximatelyannular distribution, which surround a fuel feed duct lying within thiscombustion gas feed duct and are intended to ensure that the incomingfuel and the combustion gas are mixed in that they are adjustable inrespect of their radial and/or tangential discharge direction. Practicaloperation has shown that the desired good mixing between combustion gasor combustion air and fuel can be achieved only to a very unsatisfactorydegree. In this connection, above all the secondary combustion air(secondary air) introduced separately into the combustion zone andflowing towards it in the outer circumferential region of the burner isusually insufficiently incorporated into this mixture of combustiongas/combustion air and fuel.

The prior patent application EP-A-0 974 552 relates to a burner forpartial oxidation of hydrogen sulphide for the formation of sulphurvapour. The burner comprises a plurality of tube walls arranged radiallyspaced with respect to one another and coaxially one inside the other,which bound a plurality of separate feed ducts of approximately annularcross-section for combustion gas and fuel with hydrogen sulphide. Theoutermost annular feed duct is provided for fuel containing hydrogensulphide. The discharge region of the burner is arranged in an orificeof the combustion zone, a further annular duct for supply of combustionair being formed by the discharge region of the burner and the orificeof the combustion zone.

The invention is therefore based on the problem of so improving anindustrial furnace having a burner in accordance with the preamble toclaim 1 that the incorporation of fuel into the combustion gas as awhole or into the combustion air as a whole, and hence the entireprocess of combustion (ignition, thorough combustion of the fuels,NO_(x) evolution, flame form and length), can be optimally influenced.

That problem is solved in accordance with the invention by thecharacterising clause of claim 1.

Advantageous constructions of the invention are specified in thesubsidiary claims.

Looking at the cross-section of the inner burner mouthpiece, in the caseof the industrial furnace according to the invention having a tubularburner the outermost annular feed duct is in the form essentially of afuel feed duct, and the combustion gas feed duct equipped with theindividual nozzles is arranged radially within this fuel feed duct. Ifthis construction in accordance with the invention is applied, forexample, to a use of this burner that is especially representative ofactual service, for instance in a rotary tubular kiln, into thecombustion zone of which oxygen-rich, pre-warmed secondary combustionair, so-called “secondary air, is supplied directly, for example, from acooler downstream of the rotary tubular kiln, in which process it flowsat least partially along or towards the outer circumferential side ofthe inner burner end section, whilst further combustion gas, especiallyso-called “primary air” is fed via the inner ring of individual nozzlesand fuel is fed through the outer annular fuel feed duct, it can readilybe appreciated that the fuel flowing into the combustion zone is blownpositively through the radially inner individual nozzles by means of theprimary air into the secondary combustion air flowing in from theoutside. This means, therefore, that the primary air (as combustion gas)flowing in. via the individual nozzles blows the fuel flowing in throughthe at least one outer fuel feed duct at least approximately radiallyoutwards towards the circumference of the burner, and hence into theincoming secondary air there, with the result that a very intensive andrapid mixing . . . [of primary air and fuel into the secondary airflowing in from the outside takes place.] furnaces or calciners, infurnaces for the calcining of lime, for the heat treatment of ores andsuchlike.

In respect of their discharge direction, the individual nozzles can beoriented not only parallel, but also at a specific angle to thedischarge direction of the fuel feed duct externally surrounding them.In this connection, it is also conceivable for the alignment angle ofthe individual nozzles to be adjustable. If the individual nozzles areoriented obliquely with respect to the discharge direction of the fuelfeed duct surrounding them, it is possible for the primary air (orprimary combustion gas) flowing into the combustion zone via theindividual nozzles to be blown so that it diverges outwardly to agreater or lesser extent. With a skewed arrangement of the individualnozzles with respect to the fuel feed duct surrounding them, acorresponding swirl can additionally be generated, so that the mixingeffect of primary air and fuel with the secondary air, and hence theinfluencing of the entire process of combustion, can be correspondinglyintensified. In accordance with the one structural alternative and basedon optimum findings, this orientation of the individual nozzles cantherefore be fixed as a basic setting, or, in accordance with the otherstructural alternative, the individual nozzles can be re-set time andagain depending on the particular conditions (either during operation,or during a stoppage).

At this point, it should be pointed out that although the at least oneouter fuel feed duct is intended essentially for feed of the appropriatefuels (liquid or gaseous or fine-grained or in powder form), it is quitepossible for a certain proportion of combustion air (in admixture withthe fuels) to be fed in through the fuel feed duct. Similarly, asrequired, a certain proportion of fuel can be intermixed with thecombustion gas fed in via the individual nozzles or with the primary airintroduced there.

The invention will be explained in somewhat more detail hereinafter withreference to largely diagrammatic drawings, in which:

FIG. 1 shows a diagrammatic longitudinal sectional view of an industrialfurnace in the form, for example, of a rotary tubular kiln, equippedwith a burner according to the invention;

FIG. 2 shows a longitudinal view, partly cut away, of the inner burnerend section (approximately corresponding to the fragment II in FIG. 1);

FIG. 3 shows an end view onto the inner burner end (corresponding toarrow III in FIG. 2).

The tubular burner 1 constructed according to the invention will bedescribed below with reference to an especially typical example ofapplication or use, namely, use on or in a rotary tubular kiln 2 for themanufacture of cement clinker. In FIG. 1, only the burner end ordischarge end 2 a of this rotary tubular kiln 2 is illustrated in a veryapproximate and diagrammatic view, that is to say, this rotary tubularkiln 2 can be constructed in any suitable manner. This discharge end 2 aof the kiln projects into a customary kiln discharge head 3, by whichthe kiln end 2 a is connected with the inlet 4 a of a cooler 4 of anysuitable kind, therefore shown only in outline in FIG. 1. As isgenerally well known and indicated in FIG. 1 by broken line arrows 5,completely calcined hot cement clinker emerging from the kiln end 2 afalls into the cooler 4, where it is cooled down by means of coolinggas, especially cooling air. At least part of the exhaust air from thecooler that has been warmed in this way is introduced as secondarycombustion air—hereinafter called merely “secondary air” —directly intothe combustion zone 7 inside the end 2 a of the rotary tubular kiln.

With its inner end section or mouthpiece 1 a, the tubular burner 1constructed in accordance with the invention projects, as is known perse, from behind and approximately axially into the end 2 a of the rotarytubular kiln, that is, into the combustion zone 7 thereof.

As indicated diagrammatically in FIG. 1, the burner 1 is supplied in theregion of its outer end section 1 b located outside the rotary tubularkiln 2 with fuel (dot-dash arrows 8) and combustion gas, especiallyprimary air (broken-line arrows 9) via corresponding feed pipes, andoptionally additionally with further firing fuels and air for firing ina manner that is known in principle.

The further construction of the burner 1 according to the invention willbe explained in detail in particular with reference to FIGS. 2 and 3,and above all in the region of its mouthpiece 1 a. According to theseFigures, the burner 1, or rather its mouthpiece 1 a, contains severaltube walls arranged radially spaced with respect to one another andcoaxially one inside the other, namely, an outer tube wall 10, a firstinner tube wall 1 lying coaxially and inside this outer tube wall 10 andat least one further second or central tube wall 12 lying coaxiallyinside this first inner tube wall 11. These tube walls 10, 11, 12 bounda plurality of separate feed ducts of approximately annularcross-section, that is, an outer annular feed duct 13, an inner annularfeed duct 14 lying coaxially inside this outer feed duct 13 and at leastone further inner feed duct 15, which in this case can be in the form ofa feed duct 15 of approximately circular cross-section inside thecentral tube wall 12, for example, for ignition burners or the like, notillustrated more specifically here as they are known per se. In thefront end 14 c, facing into the combustion zone 7, of the inner feedduct 14 constructed essentially for supply of combustion gas, that is,in the present case for supply of primary air (arrows 9), there isarranged a number of individual nozzles 16, distributed approximatelyannularly, as indicated in FIG. 3; as will be mentioned again later,these nozzles are retained fixedly or adjustably in an annular end wall17, which is fixedly mounted on or in the front end 14 c of the primaryair feed duct 14.

In the case of this burner 1 according to the invention, the outer (oroutermost)—looking at the cross-section of the mouthpiece 1 a—annularfeed duct is essentially in the form of a fuel feed duct 13, whilst, asalready indicated previously, the combustion gas or primary air feedduct 14 equipped with the individual nozzles 16 is arranged radiallyinside this fuel feed duct 13 (as shown in FIGS. 2 and 3).

It should also be mentioned at this point that, in modification of theexemplary embodiment described by means of FIGS. 2 and 3, it is alsopossible in principle to provide a plurality of annular fuel feed ductsand a plurality of combustion gas or primary air feed ducts, withoutdeparting from the basic principle of this inventive construction, inwhich case also the individual nozzles can be provided in a plurality ofannularly arranged groups of individual nozzles lying coaxially withrespect to one another. It should also be emphasized that any desired orsuitable number of individual nozzles 16 can be provided, to tie in withthe particular operating conditions, fuels etc.

The illustrations in FIGS. 2 and 3 also show that at its front endfacing into the kiln zone 7, the outer fuel feed duct 13 is expedientlyapproximately in the form of an annular nozzle (13 a) that dischargesfreely (i.e. openly and substantially unobstructed).

The individual nozzles 16 can be oriented in principle—as is illustratedin FIGS. 2 and 3 by solid lines—with their discharge direction parallelto the longitudinal axis 1 d of the burner, in order to ensure theimproved intermixing effect, described further above, of the fuel intothe combustion air, especially into the secondary air. It can also be aparticular advantage, however, for the individual nozzles 16 to beoriented as regards their discharge direction (cf. in FIG. 2 broken linearrows 9 a) obliquely, that is at a specific angle, to the dischargedirection (dot-dash arrows 8) of the fuel feed duct 13 surrounding themexternally, as is indicated merely partially and very diagrammaticallyby dot-dash line in FIGS. 2 and 3. This can be effected in a simple way,on the one hand, in that at manufacture of the burner 1 the individualnozzles 16 are fixedly mounted in a suitable basic setting (and so thatthey are exchangeable if necessary) in the associated end wall 17. Onthe other hand, however, these individual nozzles 16 can alternativelybe adjustably mounted in the associated end wall 17, for example, bymeans of a universal ball joint, such that their discharge direction canbe adjusted obliquely or skewed with respect to the discharge directionof the fuel feed duct surrounding them. In the case of an obliqueorientation, only the admission end of the individual nozzles 16, forexample, is displaced substantially radially with respect to the burneraxis 1 d. In the case of a skewed orientation of the individual nozzles16, the admission end of the individual nozzles 16 is moved on aconcentric circle about the burner axis 1 d. These adjustment options ofthe individual nozzles 16 are not illustrated more specifically in thedrawings, since they belong generally to the state of the art, that is,these individual nozzles 16 can be adjustably retained for instance inthe manner known, for example, from DE-A-1 96 48 981.

What is claimed is:
 1. A tubular burner for industrial furnaces,comprising: an inner end section projecting into a combustion zone ofthe furnace supplied with secondary combustion air; a plurality oftubular walls arranged radially spaced with respect to one another andcoaxially one inside the other, which bound a plurality of separate feedducts of approximately annular cross-section for combustion gas andfuel; wherein in the front end, facing into the combustion zone, of atleast one feed duct constructed essentially for supply of combustiongas, there is arranged a number of individual nozzles distributedapproximately annularly; and wherein, viewed in cross-section of theinner burner end section, at least one outer annular feed duct isconstructed essentially as fuel feed duct and the combustion gas feedduct equipped with the individual nozzles is arranged radially insidethis fuel feed duct.
 2. A burner according to claim 1, wherein at itsfront end facing into the furnace combustion zone, the fuel feed duct isapproximately in the form of a freely discharging annular nozzle.
 3. Aburner according to claim 1, the combustion gas feed duct is providedessentially for the feed of primary combustion air (primary air) and/orselectively for the feed of combustion gas or a primary air-combustiongas mixture.
 4. A burner according to claim 1, wherein the individualnozzles arranged in annular distribution are retained in an annular endwall mounted at the front end of the combustion gas feed duct.
 5. Aburner according to claim 4, wherein the individual nozzles are orientedin respect of their discharge direction parallel to the dischargedirection of the fuel feed duct surrounding them externally.
 6. A burneraccording to claim 4, the individual nozzles are oriented in respect oftheir discharge direction at a specific angle to the discharge directionof the fuel feed duct surrounding them.
 7. A burner according to claim4, wherein the individual nozzles are adjustable in respect of theirdischarge direction at a specific angle to the discharge direction ofthe fuel feed duct surrounding them.